1. Field of the Invention
The present invention relates to an electroacoustic transducer and more particularly to an improved cylindrically configured phased array transducer for transmitting and receiving acoustic signals.
2. Description of the Prior Art
Acoustical transducer arrays comprising a number of individual cylindrical electroacoustic transducer elements, typically arranged in axial alignment, for providing predetermined radiation and response patterns are well known and are used to a considerable extent in both active and passive sonar and sonobuoy systems. Transducer arrays which operate to provide a directional acoustical radiation and response pattern in a vertical plane or in a plane containing the longitudinal axis of the array are advantageously used in such systems since they can provide greater radiated acoustical energy and/or improved receiving sensitivity, in directions broadside the array, i.e. substantially perpendicular to the array axis, in the vertical plane, with an accompanying improvement of detected signal to noise ratio. Broadside vertical pattern directivity can also provide a reduction in undesired effects caused by acoustic reflections transmitted and/or received from the top and bottom surfaces of the water body in which the array is operated.
The basic criteria for broadside acoustic beam forming is well known in the art and in general requires a predetermined number of individual active transducer elements spaced apart predetermined distances and operated at predetermined relative amplitudes and phases for providing a desired directivity. In prior in-line or stacked multielemement arrays the relative amplitude and phasing of the individual transducer elements are generally obtained by electrical circuit means while maintaining the predetermined physical spacing of the elements. In such prior art arrays using piezoelectric transducer elements amplitude control or amplitude shading of the elements are also obtained by adjusting the electrode area of the various elements.
Numerous underwater detection systems exist which utilize electroacoustic transducer element arrays having both vertical and horizontal directivity patterns. One such prior art transducer array provides vertical directivity in combination with a directional and an omnidirectional horizontal pattern and comprises a number of individual vertically stacked hollow cylindrical shaped piezoelectric electroacoustic transducer sections or elements. Each one of the elements is in itself an active piezoelectric electroacoustic transducer element. Certain of these individual elements are polarized and provided with electrodes so as to provide a directional horizontal pattern while others are polarized and electroded to provide an omnidirectional horizontal pattern. Broadside vertical directivity of this prior art array is provided by proper electrical phasing and physical spacing of the respective individual directional and omnidirectional transducer elements.
Directional pattern symmetry of these prior art arrays require exacting uniformity of not only the homogeneity and physical dimensions of the piezoelectric material, but also of the manufacturing processes involved for each one of the individual transducer elements used in the array. This required matching of the individual piezoelectric elements is especially critical in multielement arrays which provide both broadside vertical directivity and omnidirectional and sine-cosine like horizontal directivity patterns for use in detection systems which use electrical output signals from the array to compute target bearing information. In addition, when uniformity between a number of individual transducer arrays of the same type is required, these control and matching problems, become even more severe. This inherent matching requirement of these prior art multielement stacked arrays and the relatively large amount of piezoelectric material required to manufacture a single transducer array results in an array of relatively high unit cost. When these prior art multielement arrays are used in an expendable and high value engineered sonobuoy, the cost of the array can represent a sizeable amount of the total cost of the sonobuoy. Also, the arrays are relatively heavy due to the number of piezoelectric elements required.